When a well penetrates a subterranean fluid-producing formation, the formation penetrated may have one of several different physical characteristics. When it is highly permeable and of an unconsolidated nature, the produced fluids can be expected to contain some particulate matter, generally referred to as sand. It is, of course, undesirable to produce such particulate matter with the production fluids because of abrasion of production tubing, valves and other equipment used. In addition, the sand could produce flow restrictions or even plugging of the fluid passageways. It is therefore necessary in such instances to avoid production of such sand and other particulate matter with the fluids. In other instances, the formation may have a low permeability which would result in low production levels. In such instances, it is necessary to take measures to increase the flow of fluid from the formation.
The co-production of fluid and sand from the formation can be reduced by "gravel packing" the well during completion operations. Gravel packing includes providing on the production conduit or tubular work string a device, including a slotted or ported cylindrical shaped member, which prevents the passage therethrough and into the interior of the conduit of solid particles exceeding a predetermined size. Such devices are incorporated into equipment and methods wherein gravel packing is introduced into an annular area between the production conduit or work string and the casing of the well, with the gravel being deposited longitudinally and exteriorly of the slotted or ported cylindrical member.
Gravel packing of wells, extending into loosely consolidated permeable formations, also has been accomplished utilizing a "pre-pack" device. The pre-pack device comprises gravel, glass beads, bauxite or other solid particulates disposed between an outer member and an inner ported member. Typically, the outer member is a stainless steel wire mesh screen. The device is affixed to the end of a production conduit and lowered into the well adjacent a production zone to prevent particulate matter, produced with the production fluids, from entering the interior of the conduit. Such pre-packs may be used alone or in conjunction with apparatus and method wherein the well bore also is gravel packed.
When the producing formation is of a more consolidated, less permeable nature, a different problem is presented. The low permeability results in low production levels of the fluid of interest. To enhance the flow of fluids from such a formation, methods have been developed for fracturing the formation to provide passageways for the flow of fluids therethrough. A typical fracturing method comprises pumping a fracturing fluid down a well bore and into the formation. The fluid is introduced at a pressure above that at which the formation will fracture. This forms one or more channels (i.e., failures or fractures) in the formation through which fluids can flow. In most instances, a proppant (e.g., sand) is included with the fracturing fluid to keep the fracture open after the formation fracturing pressure is reduced.
Another method of increasing the productivity from more consolidated formations having a low permeability is to use an explosive charge. A disadvantage of this method, however, is the heat and explosive nature of the charge can damage the casing, cement, or formation in areas where fractures are not wanted. In addition, since the fractures created are not propped open, they may close quickly after the pressure decreases.
Frequently the foregoing methods provide only a short-term effect, and the daily production dwindles over a period of months to a level at which production is no longer economically practical. Accordingly, while the foregoing methods have provided some benefits in obtaining production from difficult formations, there still is need of further improvements. More particularly, there is a need for a method of enhancing production and controlling sand, which method should have a sustained lasting effect.